The present invention relates to hydrostatic transaxles intended primarily for use in the lawn and garden industry on riding lawnmowers, lawn and garden tractors and the like.
Hydrostatic transmissions transmit rotary mechanical motion, typically from an internal combustion engine, to fluid motion, typically oil, and then back to rotary mechanical motion to rotate a pair of drive axles in order to drive the vehicle. The hydrostatic transmission controls the output rotary mechanical motion such that varying output speeds in the forward and reverse directions are possible with a single speed input rotary mechanical motion.
Such transmissions have utilized radial piston pumps and motors, axial piston pumps and motors and hybrid transmissions wherein the pump may be of the radial piston design, for example, and the motor formed as a gear pump. The speed of the output of the transmission is typically controlled by varying the eccentricity of the pump track ring or swash plate.
In recent years, it has been common practice to integrate the hydrostatic transmission within the axle housing that also contains the differential and bearings for the two axles. Such housings are typically split along a horizontal plane containing the axis of the axles, and the housing itself is formed of only two parts. Prior designs have also utilized housings having three or more components wherein the housing components attach to each other along vertical split lines or horizontal and vertical split lines.